The present invention provides an arrangement for charging energy in an energy-storing arrangement such as an ignition capacitor in an electronic ignition system, which energy-storing arrangement is connected to the secondary side of a transformer, the primary side of which is connected to a direct-voltage source in series with a first breaker controlled by a pulse train.
Energy-storing arrangements of the ignition-capacitor type are used in, among other things, the functional part of projectiles in order to ignite the functional part after an ignition pulse has been received. For safety reasons, it should only be possible to charge the ignition capacitor when a number of environmental conditions have been fulfilled. One environmental condition can be that the projectile has been exposed to an acceleration pulse of a certain magnitude. Another can be that the projectile has begun to rotate. To handle the problems of environmental conditions, there is normally a number of mechanical and/or electrical breakers between the batteries for the ignition capacitors"" charging and the ignition capacitor itself.
According to GB 2 169 994 A, a first example of a charging arrangement is previously known. According to this patent document, a transformer is used to increase the battery voltage before it charges up, for example, an ignition capacitor. In series with the primary winding of the transformer, a plurality of breakers is inserted which are controlled by environmental conditions. There is also a breaker, which is controlled by a pulse train in order to generate an alternating voltage on the primary side of the transformer. The breakers controlled by environmental conditions operate with normal direct-current signals.
A similar charging arrangement is also known from U.S. Pat. No. 5,476,044. A breaker, which is supplied with energy from the secondary side of the transformer, opens and closes the feed of the primary side of the transformer in order to form low-voltage pulses through the primary winding of the transformer from the direct voltage from the direct-voltage source on the primary side. Environmental conditions control the breakes in series with the primary winding of the transformer. The breakers controlled by environmental conditions operate with normal direct-current signals.
A breaker of the type given in known charging arrangements according to the above is controlled by direct voltages. In the case of a fault in, the control electronics, a breaker can therefore be closed without corresponding environmental conditions being fulfilled.
It is the object of the present invention to provide a charging arrangement where the risk of a malfunction is considerably reduced in relation to known charging arrangements with direct-voltage-controlled breakers.
The object of the invention is achieved by an arrangement characterized by the following, for generating the pulse train for controlling the first breaker, a signal generator and a frequency device connected to the signal generator controlled by environmental conditions of the ignition system, are included. The charging arrangement according to the invention generates the pulse train as a result of the environmental conditions which control the frequency of the pulse train which is coupled to the control of the first breaker connected in series with the primary winding of the transformer. In the charging arrangement according to the invention, therefore, it is no longer necessary to have breakers controlled by environmental conditions in series with the primary winding. The problem with malfunctions in direct-current breakers has thus been eliminated. However, this does not exclude a use of other breakers in series with the primary and secondary winding of the transformer as in GB 2 169 994 A.
The signal generator advantageously comprises the clock of the ignition system which normally operates within a suitable frequency range for being divided down in frequency. For example, the clock can operate with a frequency of 10 MHz, which is divided down to a frequency range of 10-100 kHz. Using the clock of the ignition system also means that the cost for a separate component as well as space can be saved.
According to an advantageous embodiment, a band-pass filter is coupled in between the frequency divider and the control input of the first breaker in order to attenuate signals outside a specified operating interval. The operating interval can be set to be narrow if the clock and the frequency divider operate with a great accuracy and only a specific state of environmental condition is accepted. Alternatively, the bandwidth of the band-pass filter can be increased in order to allow, for example, several specific states of environmental condition.
To further increase the safety in the ignition system, a second breaker is coupled in between the output of the frequency divider and the control input of the first breaker according to another advantageous embodiment.
According to a first further development of the embodiment with a second breaker, a control element is arranged to check the environmental conditions of the ignition system and, based on the result of the check, to control the second breaker to the closed position with approved environmental conditions and to the open position with environmental conditions which are not approved. The checking element advantageously consists of logic circuits.
According to a second further development of the embodiment with a second breaker, a frequency comparator arrangement is arranged to measure the frequency on the output side of the frequency divider and to control the second breaker to the closed position within frequencies which are suitable for the frequency divider and to the open position outside frequencies suitable for the frequency divider. The frequency comparator arrangement can advantageously comprise a frequency calculator for determining the frequency at the output of the frequency divider, a memory for storing frequencies which are suitable for the frequency divider and a comparator circuit for comparing the frequency found with suitable frequencies and controlling the second breaker on the basis of the result. Alternatively, the frequency comparator arrangement can comprise a first monostable multi-vibrator in series with a first D flip-flop and a second monostable multi-vibrator in series with a second D flip-flop, which first multi-vibrator is designed with a pulse length defining a lower limit frequency and which second multi-vibrator is designed with a pulse length defining an upper limit frequency for the current frequencies of the frequency divider. For determining the pulse lengths of the multi-vibrators, a resistor and a capacitor is advantageously arranged at the input of each multi-vibrator. The plausibility of the frequency of the pulse train is checked in a simple manner and the pulse train is only connected through if its frequency is determined to be plausible.
According to yet another advantageous embodiment, the primary side of the transformer comprises a winding with a centre tap connected to the direct-voltage source, which winding is connected symmetrically in series with the first breaker and a further breaker. This embodiment produces a symmetric feeding of the primary side of the transformer.